Field of the Invention
The present invention relates to an image pickup apparatus including an AD (analog to digital) converter.
Description of the Related Art
The readout speed of an image pickup apparatus (solid-state image pickup apparatus) has been required to be increased. This is because a fast readout speed of the image pickup apparatus can increase the number of pixels to be read and improve a readout frame rate. To increase the readout speed of the image pickup apparatus, an AD (analog to digital) converter included in the image pickup apparatus, in particular, is required to be speeded up.
Japanese Patent No. 4928069 discloses an image pickup apparatus including an AD converter in each readout row of a pixel portion.
With a configuration disclosed in Japanese Patent No. 4928069, a fast multi-bit AD conversion is effectively performed by increasing a clock frequency supplied to the AD converter, thereby shortening a time needed for the AD conversion. However, a higher clock frequency results in an increased power consumption of the image pickup apparatus.